Via Science Daily, and published in manuscript form in the journal Genome Biology, a report on the genome sequencing of a sulfate-reducing bacterium. Now ordinarily, the sequencing of a bacterial genome has become so commonplace, it almost isn’t news anymore, however I honed right in on this one: Desulfovibrio vulgaris. This bacterium is a member of an ubiquitous family of Gram negative curved rods that are found in a number of terrestrial and aquatic (freshwater and marine) environments. I became familiar with genus Desulfovibrio in junior high school when visiting my father’s microbiology lab at the University of Delaware. He, along with his collaborators, studied the related bacterium Desulfovibrio africanus. BIO230 students may complain about some of the smells generated by family Enterobacteriaceae in lab, however that stench pales in comparison to the
sulfur sulfide produced by sulfate reducers. When D. africanus cultures were being grown in Wolf Hall, everybody in the building knew about it! Read the rest of this entry
Our discussion on microbial nutrition and growth ended with a hypothetical experiment: a flask of rich culture media broth at optimal temperature was inoculated with Escherichia coli, and samples were removed at various time intervals post-inoculation for cell number determination. This experiment, once it was plotted on semi-log graph paper, allowed us to demonstrate the characteristic phases of microbial growth.
During lag phase, the E. coli cells are adjusting to the new environmental conditions (extremely abundant nutrients, no waste products to inhibit growth) by producing the enzymes that they will need to carry out metabolic pathways. In exponential phase, microbial growth is occurring at the highest possible rate possible for the given culture conditions. The maximal growth rate is determined by the richness of the culture media (a rich, complex medium will produce a faster growth rate than a simple, defined medium), and whether the temperature, pH, and osmotic pressure are all at optimal values. As the nutrients in the culture begin to be limited by the increasing cell number, cellular division is offset by cell death, and stationary phase ensues. It is important to note that cell growth is still occurring, just not at the rate observed previously. As conditions in the culture continue to diminish in death phase, cellular growth is completely offset by cellular death. Read the rest of this entry